1. Field of the Invention
The present invention relates to a photomask which is used in the manufacturing process of semiconductor integrated circuit device or a liquid crystal display, as well as a method of test/repairing, of manufacturing and of using said photomask.
2. Description of the Prior Art
Recent years have witnessed increased use of electron beam exposure apparatus of a variable shaped beam vector scan type in the manufacture of photomasks.
FIG. 13 is a schematic diagram of an electron beam exposure apparatus of a variable shaped beam vector scan type. In FIG. 13, 101 is an electron beam exposure apparatus of a variable shaped beam vector scan type. 102 is a LaB.sub.6 electron gun, 103 is a first shaping aperture, 104 is a first shaping lens, 105 is a first shaping deflector, 106 is a second shaping lens, 107 is a second shaping lens, 108 is a reducing lens, 109 is a blanking electrode, 110 is a deflector, 111 is a condenser lens, and 112 is a drawing field.
113 is a variable shaped lens which comprises the first shaping aperture 103, the first shaping lens 104, the first shaping deflector 105, the second shaping lens 106, and the second shaping lens 107. 114 is a convergent reflecting lens which comprises the deflector 110 and the condenser lens 111. 115 is a photomask which acts as the object to be exposed and which is placed on a stage (not shown).
As shown in FIG. 14A, when the electron beam exposure apparatus of a variable shaped beam vector scan type 101 is drawing circuit patterns, a method is used by which the layout data for the circuit pattern is separated into simple rectangles and each rectangle is exposed in order. As a result, the electron beam exposure device of a variable shaped beam vector scan type 101 displays high throughput when the layout of circuit patterns is simple in comparison to a complicated circuit pattern layout. This is because a simple circuit pattern layout ensures that the number of rectangles to be exposed is small even if the area to be exposed in the same.
Furthermore the electronic beam exposure apparatus of a variable shaped beam vector scan type 101 displays considerable advances in throughput in comparison with electron beam exposure devices of the following types:
electron beam exposure devices of a Gaussian beam raster scan type as shown in FIG. 14B which are adapted to use a method of drawing a circuit pattern by scanning the entire photomask, including sections to be exposed and sections not to be exposed with a Gaussian beam or PA1 electron beam exposure apparatus of a Gaussian beam vector scan type which are adapted to use a method of drawing a circuit pattern by scanning only those sections which will be exposed with a Gaussian beam as shown in FIG. 14C.
In recent years, due to the attempt to pack complicated functions in a small area which is associated with the highly integrated LSI circuits, the tendency to use wiring which runs in a curved direction is increasing as the degree of freedom with wiring running only in crosswise directions is small.
However the electron beam exposure apparatus of a variable shaped beam vector scan type 101 is not comprised of first and second shaping sections which can draw curved lines. Thus when the electron beam exposure apparatus of a variable shaped beam vector scan type 101 draws circuit patterns for polygons containing oblique lines, firstly as shown in FIG. 14A, layout data for circuit patterns of polygons which contain oblique lines are converted to polygon data, the entirety of which is formed by a plurality of rectangles and in which oblique lines are represented in stepwise form by a plurality of long thin rectangles which have the same resolution as the electron beam exposure device 101. In other words, the width W of a oblique line is set so as to equal an integer multiple of the resolution Rw of the electron beam exposure device 101. Layout data for polygon circuit patterns containing oblique lines are converted to polygon data, the entirety of which is formed from a plurality of rectangles and in which a curved line is represented in a stepwise manner by a number Nw of individual rectangles defined as Nw=W/Rw. Thereafter polygon circuit patterns containing oblique lines are drawn by exposing the rectangles one at a time.
When the layout data is evenly compressed, rectangular layout data can be accurately placed on a grid. It is not certain however that layout data for polygons containing oblique lines can be accurately placed on a grid. When layout data can not be placed accurately on a grid after shrinkage, a rounding-off error is generated in the layout data which results in reduced drawing accuracy.
FIG. 15 is a projection exposure apparatus for the manufacture of liquid crystal displays or semiconductor integrated circuit devices using a photomask which is manufactured using an electron beam exposure apparatus. In FIG. 15, 201 is a projection exposure apparatus, 202 is an Hg lamp which is used as a light source, 203 is a first lens, 204 is a first mirror, 205 is a second lens, 206 is a fly's eye lens, 207 is a two dimensional light source, 208 is a third lens, 209 is a blind, 210 is a fourth lens, 211 is a second mirror, 212 is a fifth lens, 213 is a sixth lens, 214 is a pupil plane, 215 is a seventh lens.
216 is a photomask, 217 is a wafer which acts as a object to be exposed, 218 is light which is emitted from the Hg lamp, 219 is diffracted light which is diffracted by the photomask 216.
The resolution Rp of the projection exposure apparatus 201 is defined as Rp=k1.multidot..lambda./NA where .lambda. is an exposure wavelength, NA is a number of lens apertures and k1 is a process constant. As a result, shading patterns can not be accurately displayed on a wafer 217 which acts as an object to be exposed when the width of the shading pattern which is formed on the principal plane of the photomask 216 is below m.multidot.Rp and the outline is curled. For example, a wafer 217 is exposed by mounting a photomask as shown in FIG. 16A into a projection exposure device as shown in FIG. 15. In the center of the photomask, a shading pattern is provided with a square hole one edge of which is below m.multidot.Rp. In the above situation, the shape of the shading pattern on the wafer 217 is of the shape as in FIG. 16B.
The above process is executed when oblique lines are drawn using an electron beam exposure apparatus of a variable shape beam vector type. Thus when oblique lines are present in the circuit pattern, the period of time required to draw the circuit patterns is conspicuously lengthened, the throughput of the electron beam exposure apparatus deteriorates and the cost of the photomask increases.
Furthermore increases in the period of time for drawing result in large increases in the drift of the stage of the electron beam exposure apparatus. Dimensional errors are increased and the accuracy of the photomask is reduced.